Electric double layer capacitors include a standard example as shown in FIG. 1. This capacitor consists of an integrated body comprising two insulating gaskets 1 and 2 which have respective polarizable electrodes 5 and 6 composed of active carbon and an electrolyte received in their respective openings 3 and 4 with an ion-permeable separator 7 interposed therebetween. Collector electrodes 8 and 9 are provided on the outer side of the respective electrodes 5 and 6.
This kind of a capacitor is advantageous in that it can have a high capacitance level which cannot be attained by conventional capacitors but is disadvantageous in that its electric strength is less than a few volts.
Therefore, to raise the electric strength, a plurality of such capacitors may be accumulated and electrically connected in series. Such a capacitor is disclosed in Japanese Patent Application Disclosure No. 97770/79. This capacitor is disadvantageous in that the multilayer accumulation structure makes it bulky and such a structure of large size is not suitable for miniaturization. To solve this disadvantage, a structure shown in Japanese Patent Application Disclosure No. 162218/80 may be utilized.
This improved structure is shown in FIG. 2 as including first electrodes 13a and 13b and second electrodes 16a, 16b and 16c. The first electrodes 13a and 13b include polarizable electrode bodies 11 bounded by an electrically-conductive plate 12. The second electrodes 16a, 16b and 16c have a pair of polarizable electrodes 14a and 14b bounded by an electrically-conductive plate 15.
The first electrode 13a and a second electrode 16a are separated by a separator 17a interposed therebetween. The second electrodes 16a and 16b are separated by a separator 17b interposed therebetween. The second electrodes 16b and 16c are separated by a separator 17c interposed therebetween. The second electrode 16c and the first electrode 13b are separated by a separator 17d interposed therebetween. Both of the plates 12 and 15 use an electrically conductive material resulting in this structure having the disadvantage that it needs more electrically-conductive plates as more double layer capacitor cells are connected in series to raise the electric strength. The more electrically-conductive plates that are used, the more difficult are connections between cells and the provision of terminals. Furthermore, there is still some limitation on miniaturization. In addition, its structure for reception into a cell is complicated.